The present invention relates to a method of controlling a valve for a sterilizer container and a valve suitable for carrying out the method. Such valves make possible an exchange of fluid into and out of the sterilizer container within a sterilizer. The valve body of this valve is closed during the last vacuum phase while maintaining a vacuum in the container controlled via a pressure sensor and a temperature member.
Such valves are known, for instance, from U.S. Pat. No. 4,251,482 and U.S. Pat. No. 4,228,914. As compared with known double check-valve arrangements of other sterilizer containers they have the advantage that the interior of the sterilizer container is in free communication, until entrance into the vacuum of the drying phase, with the interior of the sterilizer chamber so that a fluid exchange can continuously take place. The valves controlled as a function of the pressure and temperature furthermore have the advantage that after the end of the sterilization process the vacuum remains within the container.
U.S. Pat. No. 4,251,482/U.S. Pat. No. 4,228,914 show sterilizer containers having a valve, arranged in their bottoms, which is closed by a bellows-like expansion chamber. A shrinkable tube closes an opening which leads to the inside of the bellows and, upon a drop in the external pressure, the bellows expands and closes the valve. The thermal shrinkage of the tube takes place during the sterilization phase at a point in time which is not precisely defined. The closing of the valve takes place also in a manner not precisely defined in time still prior to the vacuum-drying -drying phase. The steam is not to be withdrawn through the valve but through the container lid above the seal, i.e. the lid must not close tightly during the vacuum-drying phase so that steam and moisture can be led away.
In the arrangement described in U.S. Pat. No. 4,251,482 there is provided as the pressure sensor an expansion vessel which is thermally closed in the steam sterilization phase by a shrink tube which thus blocks an inlet opening of the expansion vessel. This has the result that the pressure sensor upon introduction into the after-drying vacuum phase expands under the action of the pressure present in it. This expansion is used to displace a valve body into closed position, as a result of which the sterilizer container is sealed off. In the last vacuum phase, i.e. during the drying phase, the valve remains closed and can no longer contribute to the fluid exchange.
A drawing off of the steam phases produced by re-evaporation of the condensate must therefore take place through the container-lid seal or it is necessary to provide in addition, as described in U.S. Pat. No. 4,228,914, an additional valve which opens when a vacuum is applied to the outside of the container in order in this way to be able to withdraw the steam.
In the sterilizer container of French-A No. 2,335,239 there is again provided in the bottom a valve which in this case is brought into closed position not by a shrinkable tube but by a melting eutectic. It is completely impossible in this connection for the closing of the valve to take place in the ventilation phase since the eutectic melts during the sterilization phase B and, upon the melting, the valve is immediately brought into the closed position. The drying can in this case also again take place only via the lid seal during the vacuum-drying phase. However, the valve body is not controlled into the closing position only upon the ventilation phase. To this extent the manner of operation of the valve of the invention differs fundamentally from that of the known valve.